Stabilization of circuit output



Oct. 9, 1928.

' F. E. FAIRCHILD 16865552 STABILIZATION F CIRCUIT OUTPUT Filed O t. 1927 I :s Sheets-Sheet. 1

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FE: fiu'rdeM Oct. 9, 1928. 1,686,552

F. E. FAIRCHILD STABILIZATION OF CIRCUIT OUTPUT Filed Oct. 1, 1927 3 Sheets-Sheet- 2 100 11'0 ia WW 130 14'0 1J0 17 INVENTOR. I FEFm'kv/LL'M BY ATTORNEYS.

Patented Oct. 9, 1928.

* .ume a FRANK E. rAIncnrLn, .or RED BANK, rinwannsnmi Assreivon To AMnRIcAu TELE- ruounnnn TELEG APH" COMPANY, A CORPQBATION; on NEW YORK.

STABILIZATION or crncurr o'crr'ru'r.

name filed October 1,- 1927. semi no. 223,345;

This invention relates to oscillation generator circuits and amplifier circuits, and more particularly to such circuits including vacuum tube elements.

Tn circuits of the type named above, the inevitable variations in plate battery supply voltage cause inst-ability in the Output of the circuit. The object or this invention is to stabilize the circuit output.

An oscillation generator circuit may, of course, consist of an oscillating vacuum tube and certain associated circuits, without'any amplifying elements in'the circuit; again, it may include tubes and circuits giving one or more stages of amplification. My invention. in its broader aspect. is applicable to 7 either oi these two forms of circuit, and also,

as will appear from an examination of the basic principle involved, to other circuits,

including vacuum tube elements.

In general. the invention resides in utilizing a stabilizing circuit. which is placed be tween the osclllating tube for instance. and the output of the generator circuit. If the circuit includes an oscillating tube and amplifying elements. the stabilizing circuit is preferably placed between the." oscillating tube and the first amplifier tube. j The impedances of this stabilizing circuit arcad- 2 justed, as will befully disclosed hereinafter,

to give an output substantially unaffected by variations of plate voltage.

The invention will be clearlyunderstood when the follo'win the proposed embodimentithereofin an OS- cillation generator enceto the accompahfingrlrawing.

Figure .1 offthe drawing shows diagrammatically .an oscillation generator circuit ineluding two amplifier tubesand the-stabilizing circuit of the invention.

Fig. 2 shows schematically the impedances of the stabilizing circuit and indicates the voltages affected by adjustment of these impedances. a V

' Fig.'3' is a diagram showing by means of curves theefl'ect of various adjustments of the stabilizing .circuit outlierelation be-' tween plate voltage'variation.andffor in stance; the ratio of the amplifier input volt age to thefoscillatingltube output voltage.

'4 is a curveldiagr'am indicating the stabilizing circuit adjustment required to 91 detailed description of circuit is read with refer-q the oscillator output as-well as the final am 1 plifier output produced -by such adjustment.'j With reterence first to Fig.1, from left to right there are shown the tuned circuit TC;

the oscillating vacuum tube; the stabilizing clrcult. including the vacuum tube V with the grid battery poled asindicated, the re- 'sistance R,- and the indicated connections; an amplifier consisting of two vacuum tubes; and batteries common to all 'four vacuum tubes for voltages' It is thevariation of the supply p y g the necessary electrode voltage of the plate feed battery which v causes the instability of the generating c r cuit output and of which the output is to be made independent.

With reference to'-Figs. 1 and '2 of the drawing, the plate-filament impedance" (R5 of Fig 2) of the tube V is bridged across the oscillator output and the amplifier in put, being inth'e circuit between the oscillatf ing tube and the first amplifier tube. "This impedance is directly controlled by changes of the voltage impressed on the grid of the tubeV. The resistance R isin series between the oscillating circuit and the'tube V. In Fig. 2 and as used-hereinafter; E repre sents the voltage generated by the oscillator-this voltage being affected by varia tions of plate voltage. E represents the out-' put voltage of the oscillator circuitwhich,..-

ofcourse'. is the input'voltage of'the amplifier. and E 'represents the output voltage of the amplifierthat is, the final: output of the oscillation generator circuit shown in Fig. 1.5;

. It is readily'unders'toodfrom an examination of Fig. 2 that I i r E..'.R+R,, Therefore I V Itthus' appears thatin order that E 'may w to obtained by plotting for the various plate voltages the .quotients found from curves 1 L and K It is seen. from a comparison asthe plate voltage varies.

the" desired result can be accomplished if be rendered constant in. spite of changes of the plate battery voltage, R /(R+R must be caused to Vary inversely with E Substantially the negative voltage on the grid of the tube V and the resistance R are given the proper values. The trialmethod necessary to the -determination' of these proper values and the approximate values determined will appear from the following discussion.

7 The curves A to J of Fig. 3 show how the ratio 7 Y or the ratio ofthe oscillator output voltage to .the oscillator input voltage, varies with changes of the plate voltage for various valuesof the grid yoltage of tube V and the resistance R, a standard type of tube beingjemployed, of course, for the tests. It will .be noted that the grid voltages determining the curves are 15, 12 and 9 volts, while the values of the .dt are 10,000, 15,000 and 20,000 ohms.

' An examination of curves A to J reveals that the following two rules are generally applicable: to decrease the negative grid voltage, .the resistance R being constant,

- lowers thecurve and makes the curve more nearly horizontal; (2) to increase the value of-resistance R, the grid voltage being constant, lowers the curve without any great change in the slope of the curve.

'In Fig. 4, the top-curve K, shows how volts against plate voltages from to 150),

which condition would be desirable in the case of an oscillation generator circuit withhave the relation of the ratio out amplifying elements, it is necessary to to plate voltage as shown by the curve M,

- of curve M with the curves of Fig. 3 that a relation of cu-rve D of Fig. 3 shows diagrammatically and the'plate voltage which is close to the circuit of a grid voltage of 12'and a resistance R of 10,000; ohms. To alter the curve D so thatit will more closely approach coincidence with curve M of Fig. 4, it is required, in accordance with the rules derived from an examination of Fig. 3, to increase the slope slightly by slightly increasing the negative grid voltage-which increase involves a raising of the curveand to' lower the curve somewhat by an increase of the resistance R. Thus, it is seen that a grid voltage of about -12.5 and a value for R of about'14,000 ohms would give a curve approximating the curve M and the result would be a substantially constant oscillator output. l i I Let it be assumed, now, that the circuit includes an amplifier, as shownin Fig. 1. The curve K of Fig. 4 is obtained by plotting the ratio l f against the plate supply voltage, and accordingly indicates the gain of theamplifier. By multiplying the values for the various plate voltages as shown in curves K and L (the absolutely constant oscillator output), there may be plotted the curve N. This curve N'indicates the variation of amplifier output with changes of plate voltage if the ratio follows curve M-that is, if thestabilizing circuit has a grid voltage of 12.5 and a resistance Rvof about 14,000 ohms. This output is not constant, and therefore is undesirable. It remains to be determined what values for the stabilizing circuit will givea constant. amplifier output.

If the absolutely constant amplifier out-- put curve 0 (broken) is drawn (Fig. 4), and, for the various plate voltages, the values taken from this curve aredivided by the values taken from the curve K the broken curve P is obtained for the oscillator output, varying slightly from the curve L.

i By dividing the values of curve P by the values of curve K and plotting the results, the broken curve Q is found to represent the desired relation betweenthe ratio and the plate voltage. If curve Q iscom pared with curve M, it is discovered that the values determining curve M must, in' order to give a curve closer to Q, be changed to increase the slope slightly-re 1 quiring a-slight increase of the grid voltage of the establishing circuit, which involves. a raising of the curve.a1id to lower the curve slightly when allowance is made for the slope correction; Therefore, it will be;

seen that the ideal curve Q; Would require a grid voltage of slightly greater negative value than -13 and a resistance R slightly less than 17,000 ohms. i

It has been found that 'thebest results practicable in the easeof the circuit which includes the amplifier (with the standard tubes used in the tests) are obtained if the stabilizing circuit is adjusted to have a voltage of 13 on the grid of the tube V and a value of 17,000 ohms for the-resistance R. With these values, the stabilizing circuit acts as is indicated in Fig. 5 of'the drawing. The curves K and'K which show, respectively, the variation of E, with 'plate'voltage changes and the amplifier gain, are the same 'asthe corresponding -curves of Fig. 4. The values 'chosen give a variation'of .R /(Rl-R .s,

with plate voltage variation which roduces the variation of V 7, i

with changes of plate voltage shown by curve S. The result in the oscillator output is not absolutely constant, B, varying as 1s indicated by curves T. This variation of E however,is such that the amplifier output-that is, the final output of the oscillation generator circuit-is quite independent of changes of plate supply voltage between 120 volts and 150 volts, as shown by the curve U. This is the condition desired.

While the invention has been specifically described above, for the purpose of illustration, it is to be understood that its true scope is not limited by such description, but is defined in the appended claims.

What is claimed is:

1. In an oscillation generator circuit, a vacuum tube oscillator, a source of plate voltage therefor, a work circuit, an output circuit to which there will be applied by said oscillator an oscillating potential the amplitude of which will vary with variations of the voltage of saidplate source, said output circuit being connected to saidwork circuit, a stabilizing three-electrode vacuum tube having its plate-filament impedance bridged across said output circuit, means for producing changes in the plate-filament impedance of said stabilizing tube corresponding to the amplitude variations, of the potential supplied by said oscillator, and means for adjusting the operating characteristics of said stabilizing tube so that the variations of the plate-filament impedance thereof will substantially compensate for the amplitude variations of the potential supplied by said oscillator, whereby a resultant potential of constant amplitude will be supplied to said output circuit.

2. In an oscillation generator circuit, a vacuum tube oscillator, a source of plate tial supplied :by said of grid voltage therefor, a stabilizing three-electrode vacuum tube having its plate-filament impe dance bridged across the generator circuit, means for producingchang'e in the platefilament'impedance of said stabilizing tube corresponding to the variations of the potenoscillator, a series resistance in the :circuit, and means" for adjusting the operating characteristics of said stabilizing tubeso that 'the variations of the plate-filament lmpedance thereof will sub'-' stantially I compensate for the variations "of the potential suppliedby said oscillator,

torcircuit will be substantially constant.

whereby theoutput potential of the genera- 3. In an foscillatlonr generator circuit, a

vacuum tube oscillator, a stabilizing three,-

- electrode vacuum tube having its plate-filament impedance bridged across the generator circuit, aicommon source of plate supply voltage for said, vacuum tubes,.a source biasing voltage for said stabilizing tube,- and' a series resistance in the circuit, the

value of said series resistance andthe value ofsaid grid biasing voltage being, such that the output voltage of the generator circuit is independent of fluctuations'of the plate supply voltage.

4. In an oscillation generator circuit, a"

vacuum tube oscillator generating a voltage- E having a plate-filament impedance bridged mon source of plate supply voltage for said vacuum'tubes, a source of grid biasing volt-' age for said stabilizing tube, and a series resistance and of said grid biasing voltage being such that R,,/ (R+R varies inversely with changes of E due to fluctuations of .the

a stabilizing three-electrode vacuum tube across the generator circuit, a com- R in the circuit, the values ofR plate supply voltage, to give a constant circuit output voltage.

V 5. In an oscillation generator circuit including'a vacuum tube oscillator,a source of plate voltage therefor, a worlr circuit, an output circuit to which there will be applied by said oscillator an oscillating potential the amplitude of which will vary with variations ofthe voltage of said plate source, said output circuit being connected to said work circuit, and an auxiliary three-electrode vacuum tube having 1ts plate-filament impedance bridged across saidoutput circuit; the method of stabilizing the potential applied to the output circuit whichv consists in producing changes in the plate-filament impedthe amplitude variation'sof the potential supplied byv the oscillator and adjusting the operating characteristics of the auxiliary tube ,anCe of the auxiliarytube coresponding-to so that the variations of the plate-filament impedance thereof will substantially compensate for the amplitude variations of the potential supplied by the oscillator.

6. In an electric circuit, means for supplying alternating current, a vacuum tube amplifying device, a source of plate voltage therefor, awork circuit, an output circuit to Which there will beapplied an oscillating potential the amplitude of which Will vary With variations of the voltage of said plate source, said output circuit being connected to said Work circuit, a stabilizing three-electrode vacuum tube. having its plate-filament impedance bridged across the circuit, means for producing changes in the plate-filament impedance of said stabilizing tube crresponding to the amplitude variations of the potential appliedto said output circuit,

'- and means for adjusting the operating char,-

acteristics of said stabilizing tube so that variations of the 'plate fil'ament impedance thereof willsubstantially compensate for the amplitude variations of the potential applied to the output circuit", Whereby'a resultant potential of constant amplitude Will be 7 supplied to said output circuit.

7. In an electric circuitincluding means for supplying alternating current, a vacuum {tube amplifying device, a source of plate voltage therefor, a Work circuit, an output circuit to which there Will-be applied an oscillating potential the amplitude of Which Will vary With variations of the voltage of said plate source, said output circuit being a connected to said Work circuit,and an auxiliary three-electrode vacuum tube having its plate-filament impedance bridged across the circuit; the method of stabilizing the potential supplied to the output circuit Which consists in producing changes in the platefilament impedance of the auxiliary tube cor.-

responding to the amplitude variations of name to this specification this th day of September, 1927.

FRANK E. FAIRCHILD'. 

